/*
 * Copyright 2002-2005 the original author or authors.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.context.support;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;

import javax.servlet.ServletContext;

import org.springframework.core.io.AbstractResource;
import org.springframework.core.io.Resource;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;
import org.springframework.web.util.WebUtils;

/**
 * Resource接口对ServletContext资源的实现,解析Web应用根目录的相对地址。<br/>
 * Resource implementation for ServletContext resources, interpreting relative
 * paths within the web application root directory.
 * 
 * <p>
 * Always supports stream access and URL access, but only allows
 * <code>java.io.File</code> access when the web application archive is
 * expanded.
 * 
 * @author Juergen Hoeller
 * @since 28.12.2003
 * @see javax.servlet.ServletContext#getResourceAsStream
 * @see javax.servlet.ServletContext#getResource
 * @see javax.servlet.ServletContext#getRealPath
 */
public class ServletContextResource extends AbstractResource {

	private final ServletContext servletContext;

	private final String path;

	/**
	 * Create a new ServletContextResource.
	 * <p>
	 * The Servlet spec requires that resource paths start with a slash, even if
	 * many containers accept paths without leading slash too. Consequently, the
	 * given path will be prepended with a slash if it doesn't already start
	 * with one.
	 * 
	 * @param servletContext
	 *            the ServletContext to load from
	 * @param path
	 *            the path of the resource
	 */
	public ServletContextResource(ServletContext servletContext, String path) {
		// check ServletContext
		Assert.notNull(servletContext,
				"Cannot resolve ServletContextResource without ServletContext");
		this.servletContext = servletContext;

		// check path
		Assert.notNull(path, "path is required");
		if (!path.startsWith("/")) {
			path = "/" + path;
		}
		this.path = StringUtils.cleanPath(path);
	}

	/**
	 * Return the ServletContext for this resource.
	 */
	public final ServletContext getServletContext() {
		return servletContext;
	}

	/**
	 * Return the path for this resource.
	 */
	public final String getPath() {
		return path;
	}

	/**
	 * This implementation delegates to
	 * <code>ServletContext.getResourceAsStream</code>, but throws a
	 * FileNotFoundException if no resource found.
	 * 
	 * @see javax.servlet.ServletContext#getResourceAsStream(String)
	 */
	public InputStream getInputStream() throws IOException {
		InputStream is = this.servletContext.getResourceAsStream(this.path);
		if (is == null) {
			throw new FileNotFoundException("Could not open "
					+ getDescription());
		}
		return is;
	}

	/**
	 * This implementation delegates to <code>ServletContext.getResource</code>,
	 * but throws a FileNotFoundException if no resource found.
	 * 
	 * @see javax.servlet.ServletContext#getResource(String)
	 */
	public URL getURL() throws IOException {
		URL url = this.servletContext.getResource(this.path);
		if (url == null) {
			throw new FileNotFoundException(getDescription()
					+ " cannot be resolved to URL because it does not exist");
		}
		return url;
	}

	/**
	 * This implementation delegates to <code>ServletContext.getRealPath</code>,
	 * but throws a FileNotFoundException if not found or not resolvable.
	 * 
	 * @see javax.servlet.ServletContext#getRealPath(String)
	 */
	public File getFile() throws IOException {
		String realPath = WebUtils.getRealPath(this.servletContext, this.path);
		return new File(realPath);
	}

	/**
	 * This implementation creates a ServletContextResource, applying the given
	 * path relative to the path of the underlying file of this resource
	 * descriptor.
	 * 
	 * @see org.springframework.util.StringUtils#applyRelativePath(String,
	 *      String)
	 */
	public Resource createRelative(String relativePath) throws IOException {
		String pathToUse = StringUtils.applyRelativePath(this.path,
				relativePath);
		return new ServletContextResource(this.servletContext, pathToUse);
	}

	/**
	 * This implementation returns the name of the file that this ServletContext
	 * resource refers to.
	 * 
	 * @see org.springframework.util.StringUtils#getFilename(String)
	 */
	public String getFilename() {
		return StringUtils.getFilename(this.path);
	}

	/**
	 * This implementation returns a description that includes the
	 * ServletContext resource location.
	 */
	public String getDescription() {
		return "ServletContext resource [" + this.path + "]";
	}

	/**
	 * This implementation compares the underlying ServletContext resource
	 * locations.
	 */
	public boolean equals(Object obj) {
		if (obj == this) {
			return true;
		}
		if (obj instanceof ServletContextResource) {
			ServletContextResource otherRes = (ServletContextResource) obj;
			return (this.servletContext.equals(otherRes.servletContext) && this.path
					.equals(otherRes.path));
		}
		return false;
	}

	/**
	 * This implementation returns the hash code of the underlying
	 * ServletContext resource location.
	 */
	public int hashCode() {
		return this.path.hashCode();
	}

}
